U.S. says hacker helped disrupt 300 Web attacks

Hector Xavier Monsegur helped authorities take down part of the hacking collective Anonymous and arrest eight of its members in Europe and the U.S., prosecutors said.

Photo: Michelle V. Agins / New York Times

A prominent hacker set to be sentenced in federal court this week for breaking into numerous computer systems worldwide has provided a trove of information to the authorities, allowing them to disrupt at least 300 cyberattacks on targets that included the U.S. military, Congress, the federal courts, NASA and private companies, according to a newly filed government court document.

The hacker, Hector Xavier Monsegur, also helped the authorities dismantle a particularly aggressive cell of the hacking collective Anonymous, leading to the arrest of eight of its members in Europe and the United States, including Jeremy Hammond, who the FBI said was its top “cybercriminal target,” the document said. Hammond is serving a 10-year prison term.

The court document was prepared by prosecutors who are asking Judge Loretta A. Preska for leniency for Monsegur, 30, because of his “extraordinary cooperation.” He is set to be sentenced Tuesday in U.S. District Court on hacking conspiracy and other charges that could result in a long prison term.

It has been known since 2012 that Monsegur, who was arrested in 2011, was acting as a government mole in the shadowy world of computer hacking, but the memorandum — submitted to Preska late Friday by the office of Preet Bharara, the U.S. attorney in Manhattan — reveals for the first time the extent of his assistance.

Monsegur's role emerged in March 2012 when the authorities announced charges against Hammond and others. A few months later, Monsegur's bail was revoked after he made “unauthorized online postings,” the document said without elaboration. He was jailed for about seven months, then released on bail in December 2012, and has made no further postings, it said.

The memo said that when Monsegur (who used the Internet alias Sabu) was first approached by FBI agents in June 2011 and questioned about his online activities, he admitted to criminal conduct and immediately agreed to cooperate with law enforcement.

That night, he reviewed his computer files with the agents, and throughout the summer, he daily “provided, in real-time, information” that allowed the government to disrupt attacks and identify “vulnerabilities in significant computer systems,” the memo said.

“Working sometimes literally around the clock,” it added, “at the direction of law enforcement, Monsegur engaged his co-conspirators in online chats that were critical to confirming their identities and whereabouts.”